Velocity modulation tube of the kind comprising a drift space



y 0, 1956 B, B. VAN IPEREN 2,754,448

VELOCITY MODULATION TUBE OF THE KIND COMPRISING A DRIFT SPACE Filed June 13, 1951 INVENTOR BERNARDUS BASTIAAN VAN IPEREN AGENT United States Patent O VELOCITY MODULATION TUBE OF THE KIND COMPRISING A DRIFT SPACE Bernardus Bastiaan van Iperen, Eindhoven, Netherlands,

asslgnor to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application June 13,1951, Serial No. 231,316

Claims priority, application Netherlands June 21, 1950 11 Claims. (Cl. 315-6) The invention relates to velocity modulation tubes of the kind comprising a drift space which is constituted by a conductive tube of circular section, the modulator slot and the inductor slot being formed by the intermediate spacings between this tube and conductive tubes of equal diameters, aligned with the former, one at each end thereof, the modulator slot and the inductor slot communicating with resonant cavites comprsed in the modulatorcircuit and the inductor circuit, respectively.

Tubes of the aforesaid kind are known. Eiforts are made to concentrate the electrons emanating from the cathode in order to prevent them from impinging on the Wall of the drift tube before reaching the inductor slot. If no high-frequency voltage prevails at the slots, this can be readily realized, but when using high beam currents and when the tube is used to generate oscillations of great amplitude, it is practically impossible to avoid a substantial number of electrons being drawn to the wall of the drift tube before they reach the inductor slot, owing to the diverging effect of the modulator slot. Apart from the disadvantages due to heating, the efficiency is adversely affected, since it is the most useful electrons, i. e. electrons from the bunches, which are lost. Grids, which have no diverging effect, in contradistinction to a slot, can frequently not be utilised owing to the loss of electrons impinging on the grid.

According to the invention, a velocity modulation tube comprising a drift space constituted by a conductive tube of substantially circular section, the modulator and inductor slots being formedby the intermediate spacings between this tube and conductive tubes of equal diameters aligned with the former one at each end thereof, the modulator slot and the inductor slot communicating with resonant cavities comprised in the modulator circuit and the inductor circuit, respectively, is characterized in that near the inductor slot the drift space is provided with finshaped widenings which extend approximately radially with respect to the drift space. It is thus ensured that not all the electrons having a component of motion towards the wall of the drift space are intercepted by this wall, but thatsome of such electrons are allowed to travel through the' fin-shaped widenings of the drift space towards the inductor slot. Thus the efficiency of the tube is raised. In order to avoid excessive secondary emission at the second slot edge, it is advisable to prolong the fin-shaped widenings in the conductive tube aligned with the drift space. If the width of the fin-shaped widenings is chosen at the most to be equal to the width of the inductor slot, the field distortion occurring is not excessive. The fin-shaped widenings form preferably not more than 75% of the periphery of the drift space.

If the wall of the drift tube is sufiiciently thick, it may be conically milled out, after which plate-shaped members are provided, the fin-shaped widenings being left intermediate thereof; alternatively, the fin-shaped widenings themselves may be milled out forming radially-extending tapered projections therebetween. If the Wall of the drift space is thin, the fin-shaped widenings may be formed by plate-shaped members soldered on edges of slots in the drift space. As an alternative, the drift space may be formed in a manner such that on the periphery a plurality of members of U-shaped section is arranged, their height increasing gradually from the centre of the drift space. The U-shaped members may be interconnected, so that the wall of the drift space has a toothed sectional area.

Preferably the fin-shaped widenings increase in depth from approximately the centre of the drift space onwards.

In order that the invention may be more clearly understood and readily carried into efiect, it will now be described more fully with reference to the accompanying diagrammatic drawing, given by way of example, in which:

Fig. 1 is a longitudinal sectional view of a velocity modulation tube comprising a thick-Walled drift space and Fig. 2 is a cross-sectional view thereof,

Figs. 3 and 4 are two sectional views taken at right angles to one another of a velocity modulation tube comprising a thin-walled drift space and Fig. 5 is also a cross-sectional view of a thin-walled drift space.

Referring now tofFigs. land 2, a tube comprises a cathode 1 and a concentration electrode 2 for the electrons emanating from the cathode. In line with a drift tube 3 are provided conductive tubes 4 and 5, so that a modulator slot 6 and an inductor slot 7 are formed. At these slots are provided an inductor circuit 12 and a modu; lator circuit 13 by three flat walls 8, 9 and 10, together with the outer wall 11. A collecting electrode 14 is provided. A plurality of fin-shaped widenings 15 of the drift space, gradually increasing in diameter in the direction of the inductor slot are milled out in the wall of the drift space. In the tube 5 provision is made of similar widenings 16. The milling of the widenings 15 and 16 forms radially-extending projections on opposite sides ofj each widening. The projections for the drift tube 3 are shown as the cross-hatched sections in Fig. 2 between the widenings 15. In order to reduce secondary emission, the edges of the drift tube and its prolongation are bevelled at 17 and 18. The source of the electron stream 1, 2 is enclosed by a dome-shaped glass member 25 vacuum-tight sealed to the flat wall 8 and the collecting elec trode 14 is also enclosed by a similar glass member 26 which is also vacuum-tight sealed to the tube at the wall Figs. 3 and 4 show, in the case of a drift space having a thin wall, fin-shaped widenings formed between strips 19 of U-shaped sectional area, constituting together the drift space; strips 20 in line with the drift space are shown'in Fig. 4.

In order to prevent electrons from entering the inductor resonant cavity, the widenings may be'screened by strips 21, shown in Fig. 5, so that the drift space ha's'a,

toothed cross-sectional area and may be pressed out of a piece of sheet material.

What I claim is:

1. A velocity modulation electric discharge tube comprising means for producing a stream of electrons, means for collecting the stream of electrons, first and second cavity resonators disposed between the means for producing the stream of electrons and the collecting means, and a plurality of spaced aligned conductive tubes in cluding a drift tube defining a drift space, said spaced tubes defining a modulating slot and an inductor slot communicating with said first and second cavity resonators, respectively, said drift space being located intermediate said slots, said drift tube having a plurality of radially extending tapered projections in said drift space adjacent said inductor slot defining fin-shaped spacings therebetween 3 for reducing the number of electrons intercepted by said drift tube.

2. A velocity modulation "electric discharge tube, as

' claimed in claim 1, in which the radially extendingprojections .defining the fin-shaped spacings extend on both sides of the inductor slot.

3. A velocity modulation electric discharge tube comprising means for producing a stream of electrons, means for collecting the stream of electrons, first and second cavity resonators disposed between the means for producing the stream of electrons and the collecting means, and a plurality of spaced aligned conductive tubes including a drift tube of substantially circular cross-section defining a drift space, said spaced tubes defining a modulating slot and an inductor slot communicating Withsaid first and second cavity resonators, respectively, said drift space'being located intermediate said slots, said drift tube having a plurality of radially extending tapered projections in said drift space adjacent'said inductor slot defining fin-shaped spacings therebetween for reducing the number of electrons intercepted by said drift tube.

4. A velocity modulation electric discharge tube, as claimed in claim 3, in which the radially extending projections are uniformly disposed around the inner periphery of the drift tube.

5. A velocity modulation electric discharge tube, as claimed in claim 3, in which the radially extending projections extend from about the center of the drift tubeto the inductor slot.

6. A velocity modulation electric discharge tube, as claimed in claim 3, in which the drift tubeha's a relatively thick wall and the radially extending projections are formed by cutting out the fin-shaped spacings in the thick wall of the drift tube. V

7. A velocity modulation electric discharge tube comprising means for producing a stream of electrons, means for collecting the stream of electrons, first and second cavity resonators disposed between the means for pro- 7 .ducing the stream of electrons and the collecting means,

and a plurality of spaced aligned conductive tubes including, a drift tube of substantially circular cross-section defining a drift space, said spaced tubes defining a modulating slot and an inductor slot communicating with said first and second cavity resonators, respectively, said drift space being located intermediate said slots, said drift tube having a plurality of radially extending tapered projections in said drift space adjacent said inductor slot defining fin-shaped spacings therebetween for reducing the number of electrons intercepted by said drift tube, said drift tube having a plurality of slots disposed around the periphery thereof, and a plurality of strip-like U -shaped members being joined to the drift tube closing the slots to thereby form the radially extending portions.

8, A velocity modulation electric discharge tube, as claimed in claim 7, in which a plurality of partitions unite each adjacent pair of U-shaped members for preventing for collecting the stream of electrons, first and second cavity resonators disposed between the means for producing the stream of electrons and the collecting means, and a plurality of spaced aligned conductive tubes including a drift tube defining a drift space, said spaced tubes defining a modulation slot and an inductor slot communicating with said first and second cavity resonators, respectively, said drift space being located intermediate said slots, said drift tube having a plurality of radially extending tapered projections in said drift space adjacent said inductor slot defining fin-shaped spacings therebetween for reducing the number of electrons intercepted by said drift tube, said fin-shaped spacings having a width not greater than the width of the inductor slot.

10. A velocity modulation electric discharge tube comprising means for producing a stream of electrons, means for collecting the stream of electrons, first and second cavity resonators disposed between the means for producing the stream of electrons and the collecting means, and a plurality of spaced aligned conductive tubes including a drift tube of substantially circular cross-section defining a drift space, said spaced tubes defining a modulating slot and an inductor slot. communicating with said first and second cavity resonators, respectively, said drift space being located intermediate said slots, said drift tube having a plurality of radially extending tapered projections in said drift space adjacent said inductor slot defining fin-shaped spacings therebetween for reducing the num-. ber of electrons intercepted by said drift tube, the combined width of said fin-shaped spacings being not greater 7 than 75% of the inner periphery .of the drift tube.

7 ing slot and an inductor slot communicating with said first and second cavity resonators, respectively, said drift space being located intermediate said slots, said drift tube hava ing a plurality of radially extending. tapered projections in said drift space adjacent said inductor slot defining finshaped spacings therebetween for reducing the number of electrons intercepted by said drift tube, said radially extending projections extending and gradually increasing in depth from about the center of the drift tube to the inductor slot.

References Cited in the file of this patent UNITED STATES PATENTS 2,243,537 Ryan May 27, 1941 2,463,267 Hahn Mar. 1, 1949 2,466,064 Wathen'et al Apr. 5, 1949 2,512,887 Davies et a1. Iune27,'1950 2,547,061 Touraton et al. Apr; 3-, 1951 2,566,820 Bradley Sept; 4, 1951 

